The present invention relates to turbofan jet engines and, more particularly, to seals used to separate a high-pressure flow near the center of the engine from a lower pressure flow surrounding the former flow.
Modern aircraft use turbofan jet engines to increase efficiency and reduce noise as compared to turbojet engines. While the former engines provide these desirable results, turbofan engines also add some complexity to engine design. The rotating assembly of turbojet engines includes a high pressure compressor comprising a set of rotors that compresses a core flow of air that passes through the high pressure compressor. Some of the compressed air is bled off into a secondary cooling flow that is used to cool hotter parts of the engine. The secondary cooling flow is contained in a cooling flow cavity that is proximal to the spin axis of the rotor, and between the spin axis and the core flow.
Known turbofan engines comprise cases and rotors constructed in sections. For example, U.S. Pat. No. 5,338,152 issued Aug. 16, 1994 for xe2x80x9cArrangement for Sealing Structural Members Using a V-Shaped Insert, Particularly in the Case of Turbo-Enginesxe2x80x9d describes such a seal used at the boundary between the case sections of a turbo-engine. The seal described in the ""152 patent resides in a groove in a structural member. The groove includes sharp interior corners and the seal includes legs that angle into the corners. Such sharp corners and legs provide an adequate seal and work well in stationary structures such as engine cases.
However, due to the pressure differential between the core flow at the entry to the high pressure compressor and the secondary cooling flow at a high pressure, seals are also required at some of the boundaries between rotor sections. A known seal design, for use at such boundaries, has a xe2x80x9cVxe2x80x9d cross-section. A seal seat comprises a rectangular groove which straddles the boundary between rotor sections. The groove is on the surface of the cooling flow cavity facing inwardly toward the rotor spin axis, and has sharp (90 degree) interior corners. The ends of the legs of the xe2x80x9cVxe2x80x9d angle into the sharp interior corners of the rectangular seat.
Exemplary of the foregoing, as shown in FIG. 1, includes curvic teeth 18 that join the rotors. A seal 27 is seated in rectangular groove 28 that straddles the curvic teeth 18. The rectangular groove 28 includes sharp interior corners 29a and 29b. The seal 27 includes a first straight leg 30a and a second straight leg 30b, wherein the first straight leg 30a and the second straight leg 30b angle into the interior corners 29a and 29b. No feet are provided at the ends of the legs 30a and 30b. The rotor spins at over 25,000 RPM, and the resulting centrifugal force on the interior corners 29a and 29b by the straight legs 30a and 30b causes wear leading to fatigue failures at the interior corners 29a and 29b. 
As can be seen, there is a need for a new seal design that reduces stress on the groove corners, and prevents the resulting failures.
In one aspect of the present invention, a low stress seal is useable between sections of a rotating assembly. The seal comprises an apex; a first leg and a second leg, wherein the first leg and the second leg extend away from the apex on each side of the apex; a first foot at the end of the first leg; and a second foot at the end of the second leg, wherein the first foot and the second foot are rounded. A first volume and a second volume extend through the sections, wherein the first volume is proximal to the spin axis of the rotating assembly, a boundary between the sections is on a surface of the first volume, the surface faces the spin axis, and the surface faces away from the second volume. A first seal seat and a second seal seat are defined on the surface, wherein the first seal seat and the second seal seat are on opposite sides of the boundary between the sections, and the first foot and the second foot cooperate with the first seal seat and the second seal seat to prevent a flow from the first volume to the second volume.
In a second aspect of the present invention, a method for reducing stress in a seal groove at a boundary between rotors in a compressor of a turbofan engine comprises providing seal seats with rounded cross-sections, wherein the seal seats are within the seal grooves and the seal seats straddle the boundary between the rotors; providing a seal with rounded feet, wherein the seal includes an apex, a first leg extends from one side of the apex, a second leg extends from the other side of the apex, and the feet extend from the ends of the legs, wherein the feet are rounded inwardly and the feet cooperate with the seal seats to provide a pressure seal; and inserting the seal into the groove.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.